Common SSH Commands – Linux Shell Commands

We’ve put together some of the more frequently used linux shell commands, and organized them by name so you can easily find a command, their description and how to use it. This guide will continue to be updated and should not be considered a complete list of linux shell commands, but commands, we found, often used. If you would like to add to this guide, please email us and let us know. We know that these themselves are bash commands and not actually SSH commands but it is what most Linux newbies are looking for when searching for ‘SSH commands’.

Common Linux Shell Commandsls : list files/directories in a directory, comparable to dir in windows/dos.ls -al : shows all files (including ones that start with a period), directories, and details attributes for each file.

chmod 000 : No one can access
chmod 644: Usually for HTML pages
chmod 755: Usually for CGI scripts

chown: changes file ownership permissions
The set of 2 go in this order from left to right:
USER – GROUP

chown root myfile.txt : Changes the owner of the file to root
chown root.root myfile.txt : Changes the owner and group of the file to root

tail : like cat, but only reads the end of the filetail /var/log/messages : see the last 20 (by default) lines of /var/log/messagestail -f /var/log/messages : watch the file continuously, while it’s being updatedtail -200 /var/log/messages : print the last 200 lines of the file to the screen

more: like cat, but opens the file one screen at a time rather than all at oncemore /etc/userdomains : browse through the userdomains file. hit Space to go to the next page, q to quit

File Editing with VI commandsvi : another editor, tons of features, harder to use at first than picovi /home/burst/public_html/index.html : edit the index page for the user’s website.
Whie in the vi program you can use the following useful commands, you will need to hit SHIFT + : to go into command mode

:q! : This force quits the file without saving and exits vi
:w : This writes the file to disk, saves it
:wq : This saves the file to disk and exists vi
:LINENUMBER : EG :25 : Takes you to line 25 within the file
:$ : Takes you to the last line of the file
:0 : Takes you to the first line of the file

grep : looks for patterns in filesgrep root /etc/passwd : shows all matches of root in /etc/passwdgrep -v root /etc/passwd : shows all lines that do not match root

ln : create’s “links” between files and directoriesln -s /usr/local/apache/conf/httpd.conf /etc/httpd.conf : Now you can edit /etc/httpd.conf rather than the original. changes will affect the orginal, however you can delete the link and it will not delete the original.

last : shows who logged in and whenlast -20 : shows only the last 20 loginslast -20 -a : shows last 20 logins, with the hostname in the last field

w : shows who is currently logged in and where they are logged in from.
who : This also shows who is on the server in an shell.

netstat : shows all current network connections.netstat -an : shows all connections to the server, the source and destination ips and ports.netstat -rn : shows routing table for all ips bound to the server.

top : shows live system processes in a nice table, memory information, uptime and other useful info. This is excellent for managing your system processes, resources and ensure everything is working fine and your server isn’t bogged down.top then type Shift + M to sort by memory usage or Shift + P to sort by CPU usage

ps: ps is short for process status, which is similar to the top command. It’s used to show currently running processes and their PID.
A process ID is a unique number that identifies a process, with that you can kill or terminate a running program on your server (see kill command).ps U username: shows processes for a certain userps aux : shows all system processesps aux –forest : shows all system processes like the above but organizes in a hierarchy that’s very useful!

file : attempts to guess what type of file a file is by looking at it’s content.file * : prints out a list of all files/directories in a directory

du : shows disk usage.du -sh : shows a summary, in human-readble form, of total disk space used in the current directory, including subdirectories.du -sh * : same thing, but for each file and directory. helpful when finding large files taking up space.

Each line represents one process, with a process being loosely defined as a running instance of a program. The column headed PID (process ID) shows the assigned process numbers of the processes. The heading COMMAND shows the location of the executed process.

Putting commands together
Often you will find you need to use different commands on the same line. Here are some examples. Note that the | character is called a pipe, it takes date from one program and pipes it to another.> means create a new file, overwriting any content already there.>> means tp append data to a file, creating a newone if it doesn not already exist.< send input from a file back into a command.

grep User /usr/local/apache/conf/httpd.conf |moreThis will dump all lines that match User from the httpd.conf, then print the results to your screen one page at a time.

last -a > /root/lastlogins.tmp
This will print all the current login history to a file called lastlogins.tmp in /root/

tail -10000 /var/log/exim_mainlog |grep domain.com |moreThis will grab the last 10,000 lines from /var/log/exim_mainlog, find all occurances of domain.com (the period represents ‘anything’,
— comment it out with a so it will be interpretted literally), then send it to your screen page by page.

netstat -an |grep :80 |wc -lShow how many active connections there are to apache (httpd runs on port 80)

mysqladmin processlist |wc -lShow how many current open connections there are to mysql